An organic electroluminescence device (hereinafter, occasionally referred to as an organic EL device) can be classified by the emission principle into two types: a fluorescent organic EL device and a phosphorescent organic EL device. When a voltage is applied to the organic EL device, holes are injected from an anode and electrons are injected from a cathode. The holes and the electrons are recombined in an emitting layer to form excitons. According to the electron spin statistics theory, singlet excitons and triplet excitons are generated at a ratio of 25%: 75%. In a fluorescent organic EL device which uses emission caused by singlet excitons, the limited value of an internal quantum efficiency is believed to be 25%. A technology for extending a lifetime of a fluorescent organic EL device using a fluorescent material has recently been improved and applied to a full-color display of a mobile phone, TV and the like. However, as compared with a phosphorescent organic EL device, a fluorescent organic EL device is required to be improved in efficiency.
In contrast, in relation to a technology of manufacturing a highly efficient fluorescent-organic-EL device, there has been disclosed a technology of extracting emissions derived from triplet excitons by a phenomenon (i.e., TTF (Triplet-Triplet Fusion) phenomenon) in which two triplet excitons collide and fuse with each other to generate singlet excitons. A blocking layer that effectively induces the TTF phenomenon requires to be made of a highly electron-resistant compound serving as a layer for transporting electrons as well as having a wide gap for increasing triplet energy. In view of this point, a compound formed of a hydrocarbon ring has been considered suitable.
Patent Literature 1 discloses an organic EL device having a pyrene skeleton or an anthracene skeleton and further a substituent selected from a carbazolyl group, dibenzofuranyl group or dibenzothiophenyl group in an electron transporting layer adjacent to a fluorescent emitting layer.
Patent Literature 2 discloses an organic-EL device using a fluoranthene derivative for a blocking layer in order to effectively induce The TTF phenomenon.